1. Field of the Invention
The present invention concerns an electric furnace assembly, comprising at least one furnace wall and an elongated metallic resistor element being supported so as to extend adjacent to said furnace wall, said metallic resistor element being bent back and forth in its longitudinal direction so as to extend at a varying distance from said furnace wall between extreme positions located at relatively large and relatively small distances therefrom.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 AND 1.98
Such assemblies are generally known, e.g. as disclosed in the Swedish patent specification 389958 (Allmanna Svenska Elektriska AB), being designed for heat treatment of objects at high temperature, such as exceeding 1000.degree. C., and at high pressure, preferably exceeding 500 bar (50 MPa). In this known furnace, the elongated metallic resistor element is formed as a strip which is bent in a meander-like fashion, so that the flat resistor element is oriented with its flat side standing vertically, and the lower, longitudinal edge resting on the horizontal bottom surface of an annular ceramic body mounted at the inside of the cylindrical insulating wall of the furnace. Several annular support bodies with associated resistor elements are stacked one on top of the other so as to obtain a high power density and a uniform temperature within the furnace chamber.
In other previously known electric furnace assemblies, there are elongated resistor elements being embedded in the wall. Alternatively, coiled elements are supported by ceramic cores extending along the centre of the coil. See the KANTHAL.RTM. Handbook, Catalogue 1-a-5b-3, September 1994, illustrating various alloys, wire and strip elements and support systems for electric elements in furnaces.
Generally, in furnaces of this kind, the resistor elements are subject to thermal expansion and contraction during temperature changes. There is also a risk of permanent deformation, so that the dimensions of the resistor element change upon extensive use. Normally, the resistor elements are permanently elongated.